OAuth 2.0 Token Response should return 'expires_in' in seconds

As per https://tools.ietf.org/html/rfc6749#section-5.1

expires_in
RECOMMENDED. The lifetime in seconds of the access token. For
example, the value "3600" denotes that the access token will
expire in one hour from the time the response was generated.
If omitted, the authorization server SHOULD provide the
expiration time via other means or document the default value.

shindig's OAuth2TokenHandler returns the expires_in field in milliseconds.